1. Field of Invention
The present invention relates to positive displacement rotary microvalves and more particularly to an improved self-contained valve having a disposable feed insert, the valve being capable of controlled and repeatable and accurate dispensing of fluid materials of various types and viscosities and in various forms, such as beads, dots and the like.
2. Description of the Prior Art
Positive displacement rotary microvalves are known for dispensing fluid materials such as adhesives, epoxies, potting compounds, SMT adhesives, two part adhesives, silver and gold filled adhesives, UV curable adhesives, and solder pastes (with solids dispersed therein) and the like in a repeatable and accurate manner. Typically, these dispensers for fluid material are used in a wide variety of industries, e.g., electronic assembly and repair, form in place gasketing, component assembly and sealing, mold making, casting, tool and machine and equipment fabrication and assembly, SMT repair, and a variety of other uses.
These prior art dispensing devices typically include a gear motor which controls the rotation of a feed screw supported in a housing. Fluid is fed to the housing from an external source and, in general, air pressure is used to maintain pressure on the fluid and to force the fluid material into the housing. Supported in the housing for rotation by the motor is a feed screw or auger which urges the fluid material into a dispensing tip which is affixed to the output end of the housing. The dispensing tip is essentially in the form of a pointless needle which is locked and sealed to the output end of the housing. Such units are commercially available from Techcon Systems, Inc. Of Carson, Calif. and Asymtek of Carlsbad, Calif., for example.
A valve generally of the above type is disclosed in U.S. Pat. No. 5,564,606 of Oct. 15, 1996. The valve of that patent includes a rotary screw of a variable pitch type which homogenizes low viscosity material and which compresses the material to reduce its volume. That patent also discloses a one piece housing having a sleeve located in the bore and which extends only partly up the bore area. The housing also includes a passageway formed in the housing through which the fluid flows and which is in contact with the passage wall as the fluid is urged into the bore. The portion of the bore above the sleeve may be contacted with the fluid since there is no seal between the upper portion of the bore and the sleeve, i.e., there can be back flow into the region of the bore above the sleeve. The housing also includes a screw which holds a dispensing coupling and thus the sleeve in the bore, a gasket being provided between the dispensing coupling and the lower portion of the sleeve.
It is also the case that while the prior art microvalve dispensers operate satisfactorily, there are circumstances which require improvements which can be made. For example, the dispensers are normally used continuously in assembly line and commercial operations except during lunch breaks and after a shift is over. If the material being dispensed hardens in the microvalve or degrades for any reason, then the valve has to be cleaned out and this is a difficult operation, if it can be done at all at the site. Should such hardening occur, the unit is often sent back to the supplier for cleaning and this may be expensive. The repair of such a microvalve dispenser may cost anywhere from a few hundred dollars to over a thousand dollars, depending on what has to be cleaned and/or replaced. The real problem, however, is that there may not be readily available another microvalve dispenser to use in place of the one to be repaired. The result, in the absence of an immediate replacement, is that the portion of the assembly line or that aspect of the operation may have to be shut down. With the advent of automated and robot controlled equipment, the result of a shut down or suspension of one part of the assembly line can have serious and adverse effects on other portions of the assembly operation.
It is also the case that the materials dispensed may change during the day so that later dispensed material is contaminated by that previously dispensed or is incompatible with that previously dispensed. In such a case, the contamination must be cleaned out and this, again, is difficult to do on site, if it can be done at all. This may lead to the same problems noted in the case of cleaning hardened material. In some instances, users have adopted the policy of cleaning out the microvalve dispenser at the end of the day or whenever dispensed materials are changed. This takes time and requires skilled personnel.
Whatever the problem, hardening or incompatibility, the prior art devices normally include an interior housing surface which is contacted by the fluid being dispensed. Thus, cleaning or repair may involve removing the housing from the motor and discarding it for a new or rebuilt housing and interior components. If the interior housing can be cleaned, it is usually necessary to remove it from the motor and to disassemble the housing and clean each of the parts thereof.
In the case of the valve of the patent referred to previously, the housing and valve structure are such that removal of the sleeve can be a problem, especially if the material hardens in the sleeve-bore area or in the portion above the sleeve or in the exposed passageway in the housing used to feed material into the bore.
It is thus desirable and it is an object of this invention to provide a rotary microvalve dispenser in which the interior fluid contacted surfaces can easily be removed from the housing and replaced so as to avoid having fluid contact with the housing body and thus avoid the need to send the unit back to the supplier for cleaning and/or repair due to hardening or contamination in the bore of the valve.
It is also an object to provide an easily replaceable and disposable "wet end" in a rotary microvalve dispenser which can easily be replaced on site, without the necessity of sending the unit back to the manufacturer for cleaning and/or repair.
It is also an object of this invention to provide a fluid dispenser having a disposable wet end supported in a housing wherein none of the fluid being dispensed is in contact with the interior walls of the housing or infeed passages of the housing but which contacts only the interior surfaces of the removable insert forming the wet end.
It is a further object of this invention to provide an improved microvalve dispenser for use with fluids of various compositions and viscosities and which eliminates the need for cleaning of the interior surfaces of the prior devices which are wetted or come in contact with the fluid by the use of a removable and replaceable wet end insert which is easily removed and replace on site.